We propose to investigate the interaction of plasma low density lipoproteins and high density lipoproteins with the liver cell membrane using a homologous system of porcine lipoproteins, isolated liver cell membranes and intact liver cells. We will examine the lipoprotein specificity of the membrane and will explore the lipoprotein structural features responsible for specific binding using a combination of inhibitors-and selective lipoprotein-and cell-membrane modification techniques. The lipoprotein binding reaction in liver membranes will be compared with that in porcine fibroblast membrane. We will attempt to isolate a liver cell membrane protein or glycoprotein component(s) that interact specifically with the lipoproteins, and to seek evidence for its surface location and involvement in binding in intact hepatocytes, by using antibodies to the binding component(s) as inhibitors of binding by intact cells. The studies should provide insight into the mechanism of specific lipoprotein binding in normal tissues and has relevance to the pathogenesis of atherosclerosis in humans.